Processes comprising a sour gas absorption of a hydrogen sulphide comprising gas followed by biological oxidation of the dissolved sulphides are for example disclosed in WO92/10270, WO94/29227, WO98/57731, US2008/0190844 and WO2005/092788. Such processes include the biological conversion of bisulphide into elemental sulphur by means of sulphide-oxidising bacteria in an aerobic bioreactor. Typically in such processes, a liquid alkaline absorbent that has been used for absorption of hydrogen sulphide from a sour gas stream and that comprises absorbed hydrogen sulphide, predominantly in the form of bisulphide but typically also to some extent sulphide, polysulphide and/or dissolved hydrogen sulphide, is contacted with sulphide-oxidising bacteria for conversion of dissolved sulphides (mainly as bisulphide) into elemental sulphur.
Anaerobic degradation of mercaptans like methanethiol is described by Van Leerdam, R. C., 2007. Anaerobic degradation of methanethiol in a process for Liquified Petroleum Gas (LPG) biodesulfurization, PhD-thesis Wageningen University, Wageningen, The Netherlands, ISBN: 978-90-8504-787-2. In chapter 3, pages 79-80 it is mentioned that sulfide compounds inhibit the biological methanethiol degradation.
Biological processes can be very advantageous method of gas desulphurization, especially at low to medium sulphur loads and also in cases where traditional desulphurization is not very effective. It is therefore an object of the present invention to provide a biological process which can simultaneously treat a gas comprising both hydrogen sulphide and mercaptans.